iOS 键盘出现通知

- (void)viewDidLoad {
   [super viewDidLoad];
   
   [[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(keyboardWillShow:)
                                                name:UIKeyboardWillShowNotification
                                              object:nil];
   
   [[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(keyboardWillHide:)
                                                name:UIKeyboardWillHideNotification
                                              object:nil];
}

- (void)keyboardWillShow:(NSNotification *)notification {

    NSDictionary *userInfo = [notification userInfo];
    NSValue *aValue = [userInfo objectForKey:UIKeyboardFrameEndUserInfoKey];
    CGRect keyboardRect = [aValue CGRectValue];
    keyboardRect = [self.view convertRect:keyboardRect fromView:nil];
    CGFloat keyboardHeight = keyboardRect.size.height;
    
    
}

- (void) keyboardWillHide:(NSNotification *)notification{
    
    
}

- (void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillShowNotification object:nil];
    [[NSNotificationCenter defaultCenter] removeObserver:self name:UIKeyboardWillHideNotification object:nil];

}